1. Field of the Invention
The present invention relates to a control system for automatic transmissions for vehicles. Particularly, it relates to a control system for an automatic transmission for vehicles, the automatic transmission including a hydraulic torque converter having input and output shafts thereof capable of a direct mechanical coupling therebetween with a degree of coupling in accordance with the hydraulic control pressure applied thereto.
2. Description of Relevant Art
In an automatic transmission for vehicles including a hydraulic torque converter, it is favorable from the viewpoint of possible improvements in fuel consumption and vibration reduction to provide a mechanical coupling, to thereby prevent fluid slip, when the torque converter reaches the state where its proper function of torque multiplication is no longer necessary. Though desireable at a vehicle speed as low as possible, the direct coupling if effected at a low vehicle speed will very substantially reduce the number of revolutions of an engine, and enlarge the torque variation of the engine, thus instead increasing the vibration of a vehicle body, with the result being opposite the desired reduction of vibration.
To effect the direct coupling from a low vehicle speed to achieve a favorable fuel consumption rate, while avoiding the above problem, the applicant of the present invention has already proposed a semi-direct coupling mechanism capable of increasing an engagement force thereof with the vehicle speed. According to this proposal, in a low vehicle speed range having a relatively large torque variation, the semi-direct coupling mechanism is permitted to slip little by little at peak points of the variation, thus having an attentuation effect on the vibration, so that the initially intended object has been fully achieved.
To put the proposal into practice, there has been needed a vehicle speed detector of a hydraulic type having an oil pressure output increasing in proportion to the vehicle speed. In most hydraulically controlled automatic transmissions, which are provided with such a vehicle speed detector, the proposal has been and is well applicable. However, in the cases of semi-automatic transmissions or full-automatic transmissions of electronic control types without such a vehicle speed detector, a vehicle speed detector of such type has been needed to be additionally provided. This has been a significant problem when producing automatic transmissions with the semi-direct coupling mechanism by using an existing production line.
The present invention has been achieved to favorably solve such problems.